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EXECUTIVE SUMMARY The Extreme Precipitation Study has been funded in Colorado to provide a more detailed scientific insight into both the magnitude (intensity, duration and aerial coverage) and the meteorological cause of heavy precipitation events which occur at elevations above 5,000 feet in elevation. Henz Meteorological Services (HMS) was funded to provide specific storm re-construction files which could assist in providing insight into the meteorological causes of extreme events. The purpose of the HMS study was to provide storm re-construction information on eleven specific storms and any additional storms deemed important by the Colorado Climate Center. The storm re-constructions were to provide detailed information on the meteorological causes of the events and any information available on the rainfall caused by the storms. Finally, a report was prepared which identified the crucial meteorological characteristics in the thirteen extreme precipitation events deemed important to further F'MP studies. The HMS storm re-constructions provided new meteorological insights into the June, 1921 Penrose floods; the June 16/17, 1965 Plum Cre.el< and Kiowa flash floods; the Bin Thompson/Rist Canyon and Cache La Poudre flash floods of July 31/August 1, 1976 and the Frijole Creek flash flood of July 2, 1981. Tile re-constructions supported the non- occurrence of the Cimarron flash flood of .June 1952 when combined with paleo-hydrological investigations. Aerial coverage, location of occurrence and storm total rainfall was calculated for the first time using cloud-to-ground lightning data for the Opal, Wyoming flasll flood of August 10,1990. The Opal storm is considered very important in the PMP calculation for western Colorado. Finally, two new high elevation flash floods, the Owl Creek Pass flash flood of August 21,1995 and the Pagosa Springs flash flood of AUHust 22,1995, were re-constructed as rare high elevation flash floods west of the~ Continental Divicle. HMS added three additional flash floods to the meteoroiogicalnvestigation: the July 12,1996 Buffalo Creek; May 15, 1993 Rifle/Governrnent Creek and the August 18,1991 Virginia Canyon flash floods. Quantitative investigations of the extreme precipitation atmosphere (EPA) structures which caused the investigated flash floods identified specific differences ill sub- cloud and cloud layer structure between flash flood storms east and west of the Continental Divide which occur above 6,000 fel~t in lllevation. HMS produced a quantitative comparison of meteorological components associated with the flash floods which could form the basis for differentiation of high elevation site specific local storm PMP. Based on these results HMS made several recommendations for fur/her study during Phase II of the Extreme Precipitation Study: 1. Detailed studies be performed on the Frijole Creek, Opal, Wyoming and Owl Creek Pass slorms which would provide quantitative estimates of the aerial coverage, duration and intensity of the rainfall produced by the storms. 2. A frequency analysis be performed on the climatol09ical weather data base prepared :JY Colorado State University to determine the climatological return frequency of the atmospheric structure associated with the flash flOOding events in the ex'sting storm dats base. 3. Detailed analyses be performed of the passage of Tl'Opical Storm Norma in 1970 and Tropical Storm Lester in 1994 to document the interaction belween ~;ub-c1oud and cloud layer meteorological features and terrain on the observed precipitation fields. 4. Finally, a detailed evaluation of the a serieS of flash flooding events in Clear Creek ana southwestern Boulder Counties from 1990 to 199-5 be evaluated similar to the Virginia Canyon flash flooding event to increase the data base of high elevation extreme precipitation events.